The present invention relates to a drive assembly comprising an incoming shaft, at least one outgoing shaft, a motor which is connected to said incoming shaft in order to drive said shaft.
In machines that use web type of material, for example rotary printing machines, paper is continuously unrolled from paper rolls which are arranged in a roll stand. The roll stand has some type of holder means for at least two paper rolls. The roll stand is most often equipped with some type of drive assembly, in order to, in connection with a roll changing, quickly increase the rotary speed of the new roll, from standstill, to a desired peripherical velocity, which corresponds to the existing web velocity of the paper web of the paper roll which is being unrolled. The roll stand is, moreover, equipped with a brake mechanism, in order to control the web velocity and the web tension. Other devices, such as pendulum rollers, are also arranged to control and adjust the web tension of the paper web.
A large torque is required for large paper rolls, that have a large mass-movement of inertia, in order for the paper roll to reach the desired rotary speed, especially since short times of upstart are desired. Some roll stands are equipped with rollers or a drive belt which drive the periphery of the paper roll. This leads to problems in that the outermost layer is risked to be destroyed. The outermost layer is, moreover, provided with a strip of adhesive tape, which is used to unite the end of a paper web from a previous roll with the beginning of the paper web of a new roll. The adhesive tape can not extend over the entire width of the paper web when drive rollers or drive belts are used, which means that there is
Another problem occurs when the paper roll is almost completely unrolled. The rotary speed of the roll will increase dramatically when the diameter is decreased, due to the web velocity and thus the peripherical velocity of the roll being constant. The decrease in mass-moment of inertia of the holder means and a transmission agent arranged with it, and their increase in rotation, creates an increasing requirement of torque. This requirement of torque is partly achieved by the braking moment that creates the pre-set web tension. The web tension will increase when the requirement of torque increases, if no additional contribution is made. In addition to this, the general tendency in modern printing machines is to try to keep the web tension at a relatively low but constant level, in order to get a good print quality, and in order to not risk paper burst or similar. This problem is also accentuated with today""s requirements of increasing web velocities. In order to deal with this, there would be needed an additional contribution of torque to the paper roll. The torque which is required in this situation is not as large as at the upstart of a new roll, but there is, on the contrary, a considerably larger number of revolutions needed than at the upstart.
Devices other than roll stands exist, which devices require two different gear changes with the same direction of rotation, depending on different operational conditions.
The object of the present invention is to solve the above problem complex. According to one aspect of the invention, this is achieved with a device according to the preamble, characterized in a transmission agent capable of achieving two gear changes on the outgoing shaft, with the same direction of rotation, depending on the direction of rotation of the motor.
According to one aspect of the invention, it is characterized in that the transmission agent is designed with two drive paths for transmission of the rotation of the motor to the holder means, the two paths being provided with several mechanisms for changing the direction of rotation. The transmission agent may comprise a freewheel hub for each drive path, the freewheel hubs being arranged to lock and thus transmit rotation when the rotation of the corresponding drive path corresponds to the direction of rotation of the outgoing shaft, and also to disconnect when the rotation does not correspond to the direction of rotation of the outgoing shaft.
Thanks to the design according the present invention, several advantages are attained. Depending on the operation conditions, there can either be applied a relatively large torque. For example, at the upstart of a device with a large mass-moment of inertia connected to the outgoing shaft without requiring the rotary speed to be so high, or a relatively high rotary speed can be transmitted from the motor to the outgoing shaft. For example during continuous operation or at additional contribution of power, which is required at the unrolling of paper from a roll stand when the roll is almost completely unrolled. Moreover, the device permits free rotation of the outgoing shaft when the motor not is driving the incoming shaft.
Thanks to the design with a transmission agent with two alternative drive paths, there is a possibility either to transmit a large torque at a low number of revolutions, or a small torque at a high number of revolutions, with one and the same motor.
The transmission via the two different drive paths is moreover easily achieved, when different numbers of means for changing the direction of rotation and also a freewheel hub is used, simply by changing the direction of rotation of the motor.
These and other aspects of, and advantages with, the present invention will be apparent from the detailed description of a preferred embodiment, and from the enclosed claims.